This invention relates to the determination of wear of a surface of a body and in particular relates to wear of a rubbing or frictional engagement surface of a friction couple such as a brake or clutch for a vehicle or like machine.
A friction couple is defined, for the purpose of this specification, as comprising a rubbing member having a rubbing surface and a friction material member capable of coupled motion relative to the rubbing surface when pressed into frictional engagement therewith substantially normally to the direction of said coupled motion such that a frictional engagement region extends along, and transversely to, said coupled motion direction.
An arrangement for measuring wear in a rubbing surface of a friction couple is described in WO9/17072 and the contents thereof are incorporated herein by reference. However, to facilitate a clearer understanding of the invention with regard to the friction coupling and rubbing surface, FIGS. 1(a) and 1(b) of that application are reproduced here as FIGS. 1(a) and 1(b) respectively. Referring to FIGS. 1(a) and 1(b) a wheel 10 for a rail vehicle comprises an axle 11 that defines a rotation axis 12 and a rim 13 spaced therefrom by radially extending spokes 14. The spokes are faced, on at least one axial facing side thereof, by a flat annular brake disc 15 of cast iron or steel having surface 16 against which brake pads 17 of friction material can be pressed by respective pivoted levers 18 to effect braking in conventional manner. The brake disc and pads comprise a friction couple of which the disc 15 is a rubbing member, having rubbing surface 16, and each pad 17 comprises a friction material capable of coupled motion relative to the rubbing surface, by virtue of rotational motion of the latter, when pressed into frictional engagement substantially normally to the direction of coupled motion, defining a frictional engagement region 19 of the rubbing surface which extends along, and transversely to, the coupled motion direction, that is, the swept area of the brake disc. The frictional engagement region may extend for the full radial width of the disc or less than the full width, as indicated by margins 19xe2x80x2.
It will be appreciated that in operation and as a result of successive braking operations on the vehicle, the components of the friction couple will wear. The rubbing surface of the disc, within the frictional engagement region 19 will normally wear to a much lesser extent than the friction material of the pads and any wear that does occur will normally be uniform in the direction of the coupled motion, that is, in the circumferential direction along the frictional engagement region, but may vary across the regions in a direction inclined to the coupled motion direction due to variations in the properties of, and/or braking forces exerted on, the pads of friction material.
From FIG. 1(b) it will be seen that insofar as wear is substantially uniform in the circumferential direction of coupled motion, then wear across the rubbing surface may be measured at any inclination to the coupled motion direction and not just transversely thereto (radially). It will be appreciated that if the surface wear is mapped in a truly radial direction then it will be of little consequence if successive measurements are made at different circumferential positions, for example radial paths 20 and 21, whereas if an initial mapping measurement is made along a chord 22 defined between arbitrary points xxe2x80x94x then subsequent measurements will need to be made along the same chord or sufficiently closely thereto to be correlated with the first measurement.
It will be seen from FIG. 1(a) that in a typical situation in which rubbing surface wear is to be measured, the rubbing surface is not only vertically orientated but also there is limited access for placing, as well as aligning, any measuring arrangement.
There is described in the aforementioned publication an arrangement particularly suited for measuring wear in such a rubbing surface of a railway vehicle disc brake, the arrangement including a transducer having a probe, a transducer carrier member to support it such that the probe interfaces with the rubbing surface and to scan the probe across the rubbing surface 16 along a track, such as that 22, and non-wearing lands defined in the margins 19xe2x80x2 beyond the frictional engagement region, and releasable attachment means to permit the carrier member to be positioned periodically with respect to the same part of the rubbing surface to monitor long term wear by way of the scanned transducer probe. The margin lands, which may be referred to as datum lands, define a datum plane relative to which the frictional engagement region of the rubbing surface wears. The transducer carrier is supported on such lands and scanning means define a temporary scan plane offset from the datum plane so that the transducer signals derived from scanning the lands and the frictional engagement region between the lands, representing distance of the probe-surface interface from the temporary scan plane, can be referred to the datum plane of the unworn rubbing surface.
Because of the nature of the rubbing surface, and in practice the difficulty of unimpeded access to it, the described arrangement includes an alignment template fordisposition against the rubbing surface, initially to create a pair of location recesses in rubbing surface margins outside the frictional engagement region by which the template can be re-positioned on subsequent occasions, and to define by said positioning and re-positioning a scan track against which the arrangement carder can be positioned prior to removal of the template, leaving the transducer probe to scan along the track between limits of scan denoted by the recesses.
Such an arrangement is found to work satisfactorily where there is sufficient access for both alignmenttemplate and carrier member in side-by-side relationship and where a frictional engagement region of the rubbing area is contained between surface margins that define a datum plane in which said location recesses are effected and scan track defined. That is, in operation of the above described arrangement, each scan of the transducer probe encompasses a non-wearing surface land adjacent each location recess which land acts to define a reference or datum plane when the wearing frictional engagement region is scanned.
Thus notwithstanding any difficulty in repositioning the carrier member accurately, the ability to position it against such non-wearing margins of a rubbing surface and to refer transducer probe measurements to such a non-wearing datum permits signals derived at different times to be correlated and a wear pattern established.
However, there are situations when it is difficult to obtain repeatability of positioning and correlation of measurements, such as when the frictional engagement region extends for the full width of the surface and there are no non-wearing regions and for access is restricted. Even if the transducer carrier can be positioned such that the transducer probe scans along the same track, the transducer signals, which relate the instantaneous surface position to the temporary scan plane defined by attaching the transducercarrierto that surface, become less easy to correlate with those for other attachments of the carrier.
Also, when access to the rubbing surface is limited, the ability to separately attach both an alignment template and the carrier member relative thereto may be impaired. There is difficulty in ensuring that the transducer carrier and/or alignment template is re-positioned accurately if the surface wears unevenly, notwithstanding the inherent tolerances to positioning accuracy associated with the components and operating situation.
It is an object of the present invention to provide a method of determining wear of a rubbing surface of a friction couple of the type hereinbefore defined that is less dependant on parts of the rubbing surface remaining unworn than previous methods, and to provide an arrangement for determining wear of a rubbing surface of such a friction couple. It is also an object of the present invention to provide a simplified locating template arrangement for attaching the carrier member to a rubbin g surface. According to a first aspect of the present invention a method of determining wear of a rubbing surface of a rubbing member of a friction couple, comprising said rubbing member and a friction material member capable of coupled motion relative to the rubbing surface when pressed into frictional engagement therewith substantially normally to the direction of said coupled motion, comprises the steps of
(i) defining a track across the rubbing surface in a direction inclined with respect to the coupled motion direction,
(ii) defining a datum plane substantially parallel to the rubbing surface including at least two regions spaced apart along the track direction,
(iii) locating on the rubbing surface a carrier of a scanning transducer, having a probe operable to determine instantaneous distance of a probe tip from the carried transducer, such that the located transducer defines a temporary scan plane,
(iv) scanning the transducer probe across the rubbing surface substantially along the track and deriving therefrom at a plurality of scan positions transducer signals relating instantaneous distance of the rubbing surface from the temporary scan plane,
(v) scanning the transducer probe across the datum plane defining regions and from the transducer signals thereat relating the temporary scan plane to the datum plane,
(vi) referring the transducer signals derived at said plurality of scan positions to the datum plane,
(vii) removing the transducer carrier from the rubbing surface,
(viii) subjecting the rubbing surface to wear, and
(ix) repeating steps (iii) to (viii) and, for each repeated locating of the transducer carrier on the rubbing surface, comparing the referred transducer signals with referred transducer signals of at least one preceding locating of the carrier, and is characterised by
forming the datum plane defining regions as floor regions of at least one datum recess in the rubbing surface and defining each said floor region extending transversely to the track direction by at least the locating accuracy of the transducer carrier.
According to a second aspect of the present invention an arrangement, for determining wear of a rubbing surface of a friction couple comprising said rubbing member and a friction material member capable of coupled motion relative to the rubbing surface when pressed into frictional engagement therewith substantially normally to the direction of said coupled motion, comprises (i) a transducer carrier member arranged to overlie a part of the frictional engagement region of the rubbing surface and including contact datum means adapted to bear on the rubbing surface, (ii) transducer means including transducer support means, arranged to support, with respect to the carrier member, a transducer having a probe with a surface interfacing tip and operable to provide signals related to the instantaneous distance of the frictional engagement region of the rubbing surface from the transducer support means and scanning means operable to effect production of said transducer signals with respect to a plurality of different scan positions of the probe across the rubbing surface in a direction inclined with respect to said coupled motion direction, (iii) locating means including attachment means adapted to engage releasably with the rubbing member and support the carrier member overlying said rubbing surface of said rubbing member, the carried transducer means defining a temporary scan plane, and alignment means comprising an alignment template, arranged to be positioned relative to the rubbing surface to define a predetermined track thereacross to be scanned by the transducer probe, and including positioning means operable to create or occupy at least one locating recess in the rubbing surface to facilitate, for each separate engagement of the attachment means to the rubbing member, substantial alignment of the transducer probe scan positions with the track, and (iv) signal processing means operable to produce from said transducer signals at different positions along said predetermined track an indication of the variation of distance of the rubbing surface from the temporary scan plane and, for separate attachments of said attachment means to the rubbing member, variation of wear to the rubbing surface along said predetermined track in the time interval between said attachments, and is characterised by the alignment template being arranged, with the alignment template operably positioned relative to the rubbing surface, to create in the rubbing surface at least one locating recess as a datum recess having a floor region to be scanned by the transducer probe, the locus of datum recess floor regions at a plurality of scan positions defining a datum plane, and said signal processing means being operable to determine from the transducer signals characteristic of the probe scanning said datum recess floor regions displacement of the temporary scan plane from said datum plane to permit the transducer signals obtained from the rubbing surface at said plurality of positions throughout the scan to be referred to the datum plane and comparison of transducer signals, referred to the datum plane, with corresponding transducer signals, referred to the datum plane, from a separate attachment of the carrier to the rubbing surface.
According to a third aspect of the present invention an arrangement, for determining wear of a rubbing surface of a friction couple comprising said rubbing member and a friction material membercapable of coupled motion relative to the rubbing surface when pressed into frictional engagement therewith substantially normally to the direction of said coupled motion, comprises (i) a transducer carrier member arranged to overlie a part of the rubbing surface and including contact datum means adapted to bear on the rubbing surface, (ii) transducer means including transducer support means, arranged to support, with respect to the carrier member, a transducer having a probe with a surface interfacing tip and operable to provide signals related to the instantaneous distance of the frictional engagement region of the rubbing surface from the transducer support means and scanning means operable to effect production of said transducer signals with respect to a plurality of different scan positions of the probe across the rubbing surface in a direction inclined with respect to said coupled motion direction, (iii) locating means including attachment means adapted to engage releasably with the rubbing member and support the carrier member overlying said rubbing surface of said rubbing member, the carried transducer means defining a temporary scan plane, and alignment means comprising an alignment template, arranged to be positioned relative to the rubbing surface to define a predetermined track thereacross to be scanned by the transducer probe, and including positioning means operable to create or occupy at least one locating recess in the rubbing surface to facilitate, for each separate engagement of the attachment means to the rubbing member, substantial alignment of the transducer probe scan positions with the track, and (iv) signal processing means operable to produce from said transducer signals at different positions along said predetermined track an indication of the variation of distance of the rubbing surface from the temporary scan plane and, for separate attachments of said attachment means to the rubbing member, variation of wear to the rubbing surface along said predetermined track in the time interval between said attachments, and is characterised by the alignment template positioning means including releasable clamping means operable to effect clamping of the alignment template to the transducer carrier member to permit positioning with respect to the rubbing surface together, support of the alignment template in position relative to said rubbing surface by way of the attachment means and subsequent removal of the alignment template from the attached transducer carrier.